The use of structural glued laminated timber construction started in this country with the construction of a service building at the Forest Products Laboratory in 1935 at Madison, Wisconsin. The system was not new and there were many excellent examples of its use throughout Europe. World War II, and the resultant shortage of steel, furnished the incentive to further rapid development of this type of construction and there were hundreds of hangers, drill halls, and industrial plants constructed with glued laminated lumber.
Even though the use of sheet metal connectors such as joist hangers, straps, and anchors have been in use with light wood framing lumber for many years and have become widespread in the construction industry in the last 20 years, the adoption of sheet metal connectors has been slow in developing for glulam timbers. The same heavy strap metal connectors with lag screws as were used with solid timbers has continued to be the accepted practice in glulam systems. The state of the prior art as shown in FIG. 1
Increasing labor costs in the construction of large industrial/commercial facilities has led to the need for development of new hardware in glulam systems which will meet the requirements of economy, offer speed of erection and contribute to the building's overall aesthetics.
With glulam timbers, spans of 100 feet are possible and the glulams range from 41/2" to 641/2" in depth. Ability to resist loads is dependent upon the beam remaining in an upright position. Bracing structures using 2 .times. 6 lumber members or custom designed metal strap members have been used in the past.
Current state of the art metal knee braces consist of a simple constant width strap, attached at its ends to the upper transverse member at the lower midpoint to the underside of the braced member. The braced member is held in respect to the upper transverse means by triangulation and in tension only by the action of each leg in respect to the braced lower member.
Such simple metal straps have an International Council of Building Official (I.C.B.O.) approved load value of about 750 lbs. as the actual braced value is limited by the two fasteners in the bottom of the braced member. The reason for the low load value is the fact that the load value is limited to the shear value of the lag bolts acting between the fasteners and the knee brace material.
The section of material used for the knee brace is not limiting. For example, the section called for in a typical standard knee brace is good for about 3,000 lbs. but since the I.C.B.O. approval for the brace is only about 750 lbs. as explained above, the straps of the present state of the art are very inefficient; being limited by the practical number of fasteners and required center to center and edge distance spacing as used on the bottom support member.
The attachment to the upper transverse member is not realistically limited. Considerably more area is available for code approved spacing and use of more fasteners is possible.
In summary, the metal straps of the present state of the art are inefficient because while the attachment of the mid portion of the strap as attached to the braced member is at capacity, only about one fourth of the strap capacity is used.